1. Field of the Invention
The present invention relates to a generally to a variable damping characteristics shock absorber, suitable for use in an automotive suspension system.
2. Description of the Background Art
Japanese Utility Model First (unexamined) Publication No. 61-164836 discloses a variable damping characteristics shock absorber of the type for which the present invention is directed. In the disclosed construction, an orifice is formed through a piston for generating a damping force in response to a piston stroke according to relative displacement of a vehicular body and a suspension member which rotatably supports a road wheel. An end of the flow restriction orifice is closed by a disc valve which opens and closes the end of the orifice. A fluid passage is formed through a piston rod in a parallel relationship with the flow restriction orifice. A flow control means is associated with the fluid passage for adjusting a fluid flow path in the fluid passage for adjusting damping characteristics.
In the shown construction, higher or harder suspension characteristics or a greater damping force may be generated by greater magnitude of flow restriction provided by the flow control means. By a greater magnitude flow restriction, a smaller amount of working fluid flows through the fluid passage for generating a greater fluid pressure difference at both sides of the piston and thus generating a greater damping force. On the other hand, lower or softer damping characteristics are obtained by a smaller magnitude of flow restriction for allowing a greater amount of working fluid to flow through the fluid passage. A greater amount of fluid flow through the fluid passage may reduce a fluid pressure difference at both sides of the piston for generating a smaller magnitude of the damping force.
In such construction of shock absorbers, it has been observed that, at a relatively low piston stroke speed range, the flow control means of the fluid passage is principally effective for generating a damping force. On the other hand, at a relatively high piston stroke range, the orifice is principally effective for generating a damping force. Since the orifice and flow control means have different variation characteristics of magnitude of fluid flow restriction, a smooth variation of damping characteristics is not available through relatively wide piston stroke speed range.
Furthermore, neither of the orifice nor flow control means may provide linear characteristics in varying the damping characteristics, the prior proposed shock absorber is still not satisfactory in view of an achievement of both vehicular driving stability and riding comfort at any vehicular driving condition.